function fitScreen() {
    var screenNowWidth=document.documentElement.clientWidth||document.body.clientWidth;
    var rateW=3.75;
    document.documentElement.style.fontSize=screenNowWidth/rateW+"px";

    var screenNowHeight=document.documentElement.clientHeight||document.body.clientHeight
    var a=screenNowWidth/rateW;
    var c=screenNowHeight/a;
    var main=document.getElementById("main");
    main.style.height=(c-0.94)+"rem";
}

window.onload=fitScreen;